Stents are frequently used to enlarge, dilate or maintain the patency of narrowed body lumens. A stent may be positioned across a narrowed region while the stent is in a compressed state. The stent may then be expanded in order to widen the lumen. Stents used in the gastrointestinal system are commonly constructed of plastic. Plastic stents facilitate retrieval and/or replacement of the stent during a follow-up procedure. However, plastic stents are not expandable. That is, plastic stents have a fixed diameter. Since plastic stents are frequently delivered through the working channel of an endoscope, the diameter of the working channel limits the diameter of the stent. For example, plastic stents typically have a diameter that is no greater than 11.5 French. However, such a small diameter stent rapidly becomes clogged within the biliary and pancreatic ducts, thereby requiring replacement every three months, or even sooner.
Stents constructed of various metal alloys have also been used within the biliary and pancreatic ducts. These types of metal stents may be self-expanding or balloon expandable, and are designed to expand to a much larger diameter than the plastic stents described above. Consequently, such metal stents remain patent longer than plastic stents, averaging perhaps 6 months before clogging. However, the capability of larger diameter stents to collapse into endoscopic delivery systems necessitates mesh or wire geometries which incur tissue in-growth, thereby rendering the stent permanent and impossible to remove. Therefore, even when a retrievable metal stent has been employed, it may not be possible to remove it without damaging surrounding tissues. Moreover, because these types of stents often comprise nitinol, they tend to expand during deployment. As a consequence, there can be a risk that such a nitinol stent would expand before it is properly deployed in the desired lumen region.
Coiled stents with multiple coils have also been employed. Such stents can undergo the required expansion within a targeted ductal region and remain flexible. However, such stents attain their expanded diameter by undergoing a considerable shortening of their length i.e., foreshortening. Considerable foreshortening results in difficulty deploying the stent at a precise position.
In view of the drawbacks of current stents, an improved stent is needed that is highly compressible, expandable, retrievable, and/or limits or prevents endothialization.